1. Field of the Invention
The present invention relates to a lubricating coating compound for a sliding member, a sliding structure combining two sliding members respectively having sliding surfaces held in sliding contact with each other, wherein the lubricating coating compound is applied to at least one of the sliding surfaces, and a slide bearing apparatus using the sliding structure.
2. Description of the Related Art
As lubricating coating compounds, various types are known including (i) one in which an oil-based composition is applied by spraying or the like and is used in a wet state, (ii) one in which after a coating is formed, a solvent is allowed to volatilize, and the coating is used as a dry film, and (iii) one in which a coating is allowed to cure under the normal temperature or on heating and is used as a cured film.
The lubricating coating compounds (i) and (ii) are used in the form of one kind of lubrication in which a lubricating composition is supplied to opposing surfaces of two members which slide with respect to each other on their opposing surfaces.
Namely, the lubricating film formed by each of these lubricating coating compounds (i) and (ii) is not formed in the two sliding members themselves, but is, in a word, interposed between their opposing surfaces. Accordingly, when such a lubricating film has been consumed, the lubricating film can be formed again by performing similar spraying or the like.
In contrast, the lubricating coating compound (iii) is different in kind from the lubricating coating compounds (i) and (ii). Namely, the lubricating coating compound (iii) forms a portion or portions of either one or both of the two sliding members, i.e., a surface layer of the sliding member is formed.
It is desired that this surface layer, i.e., the film which forms the sliding surface, excel in the mechanical strength, have good adhesion to a substrate, should not be damaged by an external force or worn out easily during sliding, or should not exfoliate from the substrate.
Here, the imparting of lubricity to the film, on the one hand, and the mechanical strength of the film and its adhesion to the substrate, on the other hand, are in an apparently incompatible relationship, and there is a problem in that if an attempt is made to improve the lubricity, the strength and adhesion inevitably decline.
In addition, in a combination of two sliding members held in sliding contact with each other, in a case where one sliding member, particularly its sliding surface, is formed of a synthetic resin, a metallic sliding member, such as one formed of steel, is generally used as the mating member. However, there are cases where the mating member itself is also formed of a synthetic resin or at least its sliding surface is formed of a synthetic resin in view of various purposes and needs, i.e., for the purposes of rust prevention, chemical resistance, electrical insulation, light weight, and a requirement in design.
As such an example, it is possible to cite, among others, a combination of a synthetic resin bearing and a steel-made shaft provided with a synthetic resin coating, a combination of gears each formed of a synthetic resin, and a control cable made up of a combination of a synthetic resin pipe and a wire rope which is coated with a synthetic resin, is inserted therein, and is adapted to be pushed and pulled (undergo reciprocating sliding) or undergo rotational sliding.
However, in the case of the combination of the sliding members formed of a synthetic resin, even in the case of a tetrafluoroethylene resin which is known to have a low coefficient of friction, it is difficult to lower the coefficient of kinetic friction to 0.1 or less in sliding under a dry frictional condition.
On the other hand, in a slide bearing apparatus having the function of allowing the displacement of a structure to escape through sliding in response to earthquake motion, if the coefficient of friction acting on its sliding surface is large, sliding displacement fails to be performed desirably, and effective vibration isolation fails to be demonstrated, so that it is desired that the frictional resistance at its sliding surface should be low.
Furthermore, with the slide bearing apparatus, since the apparatus does not operate other than when a force is applied thereto due to an earthquake or the like, in order to obtain a stable vibration isolation effect, it is required that the frictional resistance during operation should be stable, i.e., the change over time of the coefficient of static friction should be small. Namely, it is required that, in addition to the fact that the coefficient of kinetic friction should be low, the coefficient of static friction should also be low and stable.
However, in the case of the combination of sliding members formed of a synthetic resin, the coefficient of static friction generally shows a value which is not less than two times the coefficient of kinetic friction. Furthermore, in cases where the apparatus is under load and is normally not operated, the coefficient of static friction tends to become gradually large due to microscopic creep ascribable to the contact of the two members over a long period of time.
Accordingly, although both the coefficient of static friction and the coefficient of kinetic friction can be lowered by applying a lubricant such as grease or oil to the sliding surfaces, the lubricant comes to be discharged from the sliding surfaces over short periods of time, and its effect is lost. Moreover, the coefficient of friction gradually rises due partly to the effect of the solidification or deterioration of the lubricant over time.